#define _CRT_SECURE_NO_WARNINGS 1

#include<stdio.h>
#include<math.h>
int main()
{
	float s = 0,S = 0;
	float a = 0, b = 0, c = 0;
	float ret1 = 0,ret2 = 0;
	scanf("%f%f%f", &a, &b, &c);
	s = (a + b + c) / 2;
	ret1 = s * (s - a) * (s - b) * (s - c);
	ret2 = pow(ret1, 0.5);
	printf("%.3f", ret2);
	return 0;
}